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What are the effects of file locking on NFSv3 and CIFS clients?

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Applies to

  • ONTAP 9
  • Data ONTAP 8 7-mode

Answer

Note: There are more complex scenarios like multiprotocol access (CIFS and NFS) which are not covered here.

  • Locks set by Network File System (NFS) clients are not enforced
    • A client may gain access to a locked file, or to part of a locked file, depending on whether the client checks for and observes the lock
    • This only applies to NFSv3 using NLM, but NFSv4 has a mandatory locking infrastructure
  • Locks set by CIFS/SMB clients are enforced
    • The locks affect clients, whether or not the clients check for the locks.
    • If a lock exists, the client is denied the type of access according to the lock.
  • If running the dump command on Data ONTAP 8 7-mode, it will ignore the file lock to finish the dump or NDMP backup.
How does ONTAP keep track of locks?
  • Lock Manager (LMGR) is an ONTAP subsystem that implements file locking to manage concurrent access.
    • It keeps track of which files are open and which locks are granted.
    • This is handled in the Data/WAFL layer of ONTAP
  • Each node on an ONTAP 9 cluster has its own lock manager running that manages the volumes located on aggregates owned by that node.
    • Note: In 7-mode this is per controller
  • To accomplish these tasks, a series of memory structures (objects) are allocated to the lock manager; the amount of these structures depends on the amount of memory installed on the storage controller and is fixed.
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